Underfloor duct is an electrical raceway system designed to be imbedded in the concrete floor of offices, classrooms, laboratories, manufacturing areas, supermarkets, etc., for the purpose of providing an enclosed raceway for wires and cables from their originating panel to their point of use.
Such an underfloor raceway system includes two types of ducts, namely feeder ducts and distribution ducts. Complementing those two types of ducts are junction boxes, support couplers and supports, horizontal and vertical elbows, power and telephone outlets and numerous cast and sheet metal fittings such as conduit adapters, change of direction duct runs, "Y" take-offs, etc.
Typical examples of such underfloor duct systems are seen in U.S. Pat. No. 3,405,834 to Butler et al. and U.S. Pat. No. 3,338,450 to Rose, both assigned to the assignee of the present invention. The ducts used with systems like those shown in the Butler et al. and Rose patents typically are rectangular cross section, seamless ducts which are formed by rolling a metal sheet into the rectangular cross-sectional shape and forming a seamless weld where the edges of the sheet meet.
The prior art has also included a number of electrical raceway systems wherein the raceway is constructed from two or more components which are joined together.
U.S. Pat. No. 4,338,484 to Littrell discloses a floor duct having a generally flat bottom section, and an inverted channel-shaped top section, with flanges extending horizontally from the lower end of the legs of the upper channel section. These flanges are superimposed upon and attached to the lower section of the duct.
U.S. Pat. No. 2,931,533 to Wiesmann discloses a two-piece duct utilized with cellular metal flooring wherein the two-piece duct is formed from a flat lower piece and an inverted channel-shaped upper piece having horizontal flanges at its lower edges which are received in grooves defined in the lower piece. The sections are then welded together to form an integral unit.
Also, many cellular metal flooring systems utilize separate components to define the raceways or conduits located within the cellular metal flooring. For example, U.S. Pat. No. 3,812,636 to Albrecht et al. illustrates at FIG. 37 thereof a cellular metal flooring system having individual bottom panels for defining wiring enclosures in the raised portions of the cellular metal flooring.